A lot of what we know about tidal wetland ecology comes from extensive study of marshes on the East Coast, particularly those in the northeast and mid-Atlantic. Where would wetland science be without groundbreaking studies done in the salt marshes of New England and the Chesapeake Bay? Fewer studies have been done in the tidal wetlands of the Pacific Northwest. The first large-scale assessment of Pacific Northwest marshes, conducted in 50 Oregon coastal wetlands, found some critical differences between these marshes and their well-studied relatives in other regions. The investigators characterized plant communities and measured a suite of environmental factors that could contribute to structuring regional vegetation patterns in these marshes. Factors considered included typical water and sediment quality parameters (salinity, temperature, dissolved oxygen, etc.) and landscape characteristics in the 100m-, 250m- and 1000m-buffer zones around the marshes, as well as in the watersheds of each marsh.

The Oregon marshes differed in many respects from the paradigms developed in other areas. For example, the plant communities were substantially more diverse than northeast marshes (but comparable to those on the Gulf and southeast coasts), and the typical negative relationship between salinity and vegetation species richness was not observed. The zonation that is so characteristic of East Coast marshes was also notably absent. In addition, the authors point out that nitrogen dynamics may be substantially different as coastal upwelling and N-fixing vegetation in the estuarine watersheds of these systems provide for high levels of natural N.

The most important factor determining the particular wetland assemblages found at a site was salinity, followed by land cover in very close proximity to the site (within the 100m buffer), which suggests that managers need to prioritize conservation of natural hydrology and protection of the 100m buffer zone. It is also clear that information gathered at iconic wetlands on the East Coast may not be applicable to PNW marshes, and so more research on these systems is in order.

Oyster Reefs Now and Then: Study Models Differences between Current and Historic Filtration Rates

The decline of oyster reefs in North American estuaries has meant a loss of many things: critical habitat for a range of organisms, livelihood of oystermen, a delicious food source, and an important link in the food web of many coastal systems. Add to this list loss of a significant ecosystem service, as filter-feeding oysters contribute to water clarity and quality as they feed. A recent study used existing information about the extent of current and historical oyster reefs along with data about oyster filtration rates and relevant environmental variables to construct a model of oyster filtration. The model was applied to 13 major estuaries to compare filtration by past (1880-1910) and present (2000-2010) oyster populations.

Model outputs indicated that the filtration capacity of oysters has declined almost everywhere by a median of 85%, with the greatest and earliest declines occurring in north Atlantic estuaries. One notable exception was Apalachicola Bay in the Gulf of Mexico, where filtration capacity had actually increased, likely due to the strong management focus on maintaining the standing stock of oysters there. Generally, historical oyster stocks were estimated to be capable of filtering a volume of water equivalent to or larger than the estuary’s volume within the water residence time (termed “full estuary filtration” by the authors), whereas present day stocks cannot. Because of the “shifting baseline” phenomenon in the north Atlantic (historical data there likely represent oyster populations already in decline), none of the estuaries in that region appeared capable of full estuary filtration in either time frame.

The authors explain that while current oyster restoration projects are often measured by areal extent, oyster density and size distribution also play important roles in determining the amount of water reefs can filter. These metrics should be considered and assessed in future restoration efforts. This study also highlights the potential for managers to consider wider ecosystem service benefits alongside oyster harvests, and allows these objectives to be framed in a historic context.

The Price of Rice: Altered Hydrology in Spanish Ebro Delta Affects Macrophyte Community

The hydrology of the Spanish Ebro Delta has been subject to human modification for about 150 years, mostly for rice cultivation. These alterations have brought increases in fresh water as well as inputs of pesticide- and fertilizer-laden agricultural wastewater to coastal lagoons throughout the estuary. At the same time, cover of submersed macrophytes declined by more than 80%, the system shifted to phytoplankton-based primary production, and concomitant changes occurred in fish and waterfowl populations. A new management strategy, initiated in 1990, replaced much of the wastewater inputs with freshwater from the Ebro River, which maintained the reduced salinities in the lagoons in the months of May to November. In this study, investigators examined the effect of this relatively new management scheme on community composition, distribution, seasonal abundance, and flowering rates of submersed macrophytes in three coastal lagoons in the Ebro Delta.

A range of salinity-related effects on individual plant species and communities was observed. Peak biomasses of the dominant macrophyte species in the Delta measured during the study were 88 to 95% lower than maximum values reported in the literature at similar salinities elsewhere, and there has been little to no recovery of macrophyte species in the twenty years since the inception of the new management measures. The authors suggest that the main management actions needed to restore the natural diversity and productivity of submersed macrophytes in this system should be increasing salinity during the period of rice cultivation by reducing freshwater inputs and increasing flushing connections with bays.

Excess nutrient loading can result in phytoplankton blooms in coastal systems, but in some cases macroalgae blooms can form as well. The latter can form unsightly and stinky mats when they die and wash up on shore, but what is the ecological impact of these mats? Do they smother marsh plants like Spartina, and does their decay add an overabundance of nutrients to the marsh soil? Researchers in Rhode Island simulated macroalgal bloom/deposition events in both in situ and laboratory mesocosm experiments by adding various amounts of macroalgae to the sediment surface. Parameters related to Spartina growth and sediment nutrients were measured in both sets of experiments; benthic invertebrate communities were also assessed in the in situ experiments.

Results from the mesocosm experiments indicated that macroalgal mats significantly increased the nitrogen content of the mesocosm sediments, but not the N content of the Spartina plants themselves. Spartina growth rates were enhanced by the addition of macroalgae, but the trend was not significant, and stem density and percent Spartina cover were unchanged. In the in situ experiments, Spartina growth rate was slower in treatments with macroalgae added, but stem N content, percent cover, and grazer and predator abundance were not significantly altered.

The authors believe that a number of factors may have impacted their results, including tidal flushing or consumption of nutrients in the in situ experiments or high background N concentrations masking the signal in the mesocosms. Regardless of the reasons for the results, if macroalgal blooms intensify with rising temperatures and ongoing eutrophication, their ecological impacts will need additional study.